When you actually think about it, trying to make an entire complex being out of only 4 simple pieces isn’t very efficient. The proteins that our DNA codes for are themselves made out of amino acids, of which there are only 20. So it’s safe to say, scientists have been dreaming about expanding that toolkit for a long time. That’s right. We’ve upgraded.

This class of synthetic DNA base pairs are called xeno nucleic acids, or XNA. Biochemists first started trying to add these new base pairs to DNA in the 1980s, which as you can imagine, is not easy.

Base pair bonding in natural DNA is highly accurate--A always bonds with T and C always bonds with G, but the pairs we’ve added are harder to get right, and they tend to mispair. This is because the hydrogen bonds that hold the two sides of the DNA helix together are very weak. While they’re enough for the natural stuff, holding synthetically introduced base pairs together properly requires something a little stronger.